Electromagnetic switch



H. C. HASTINGS.

ELECTROMAGNETIC SWITCH.

APPLICATION FILED JULYB, 19x9.

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H is Attorn ey.

H. C. HASTINGS.

ELECTROMAGNETIC SWITCH.

APPLICAT ON FILED JULYH, 1919- Patented Feb. 17, 1920.

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HAMMOND CHARLES HASTINGS, OF RUGBY, ENGLAND, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTROMAGNETIC SWITCH.

Specification of Letters Patent.

Patented Feb. 17, 1920.

To all whom it may concern:

Be it known that I, HAMMOND CHARLES HASTINGS, a subject of Great Britain, residing at Rugby, in the county of Warwickshire, England, have invented certain new and useful Improvements in Electromagnetic Switches, of which the following is a specification.

My invention relates to electromagnetic switches for controlling electric circuits and more particularly to switches ofthe lock-out type, which hold open when the current in a circuit is relatively high and close when the current drops to a predetermined value.

In the starting of electric motors, it has been the practice to employ a plurality of electromagnetic switches which close successively to cut out sections of resistance from the motor circuit and bring the motor up to speed. Various means have been devised for controlling the operation of the switches so that they will only close when the current is at a proper value, that is, after a switch has operated to' cut out a section of resistance the next switch will not operate until the current has dropped to a safe value due to the speeding up of the motor.

A form of switch which has frequently been proposed for this purpose is one in which a shunt coil closes the switch and a series coil, instead of controlling the circuit of the shunt coil, positively prevents the switch from closing by actually holding'it open, that is, the shunt coil pulls a'galnst the series or holding-out coil. The diificulty with this type of switch is that the value of current in the holding-out winding at which the switch will close depends upon the pull of the shunt coil, which, of course, will vary with the voltage and also with the temperature of the coil. setting of the switch, 2'. 6., the motor current value at which it closes, changes with the change of voltage. It also closes at one value of current in the series coil when the shunt coil is cold and another when it is at its operating temperature which is ordinarily about degrees C.

The object of the present invention is to obtain a lock-out switch, which has a shunt closing and series lock-out coil, and is such that the balance between the closing and holding open forces will not be affected by In other words the.

the variation in line volts and resistance of the shunt coil referred to above.

Referring to the drawings, Figures 1, 2 and 3 are curves showing various relations of the pull due to the closing and lock-out fluxes for various Values of current in the shunt coil of the switch; Fig. 4: is a side elevation of a lock-out switch embodying my invention; Fig. 5 is an end View of the switch showing the series lock-out coil and its magnetic circuit; Fig. 6 is a part of a top view of the same; and Fig. 7 is a motor control system embodying my invention.

In carrying my invention into effect I utilize an operating magnet of the type described in the British Patent No. 11349 of 1911 and the British Patent No. 20534: of 1911 where a single magnetizing coil is used to produce two magnetic fluxes, which produce opposing forces on a single pivoted lflever, which forms part of the path for each As described in the British Patent No. 11349 of 1911 the magnetic circuits'are so proportioned that as the current changes in the magnetizing coil the percentage change in pull due to one of the fluxes is different from the corresponding percentage change in pull produced by the other flux. By changing to above, and is illustrated by Fig. 1 of this specification.

Referring to the figure it is assumed, for purposes of illustration, that the two forces act at equal radii, and that the rocking lever which carries the moving contact is in the position corresponding to contactor open. When the current in the magnetizing coil has the value OD the forces due to the two fluxes are balanced, as is indicated by the intersection of the two curves at C. At values of current less than this the force due to the flux tending to close is always greater than the force due to the other flux, and at a particular value of current such as OB, where the difference A-F in the closing and locking-out forces is just equal to the out of balance weight of the moving lever, the contactor will close. It would also close at any value of current lower than sponding to an increased value of current O-D1. It is obvious that the look-out pull may be decreased in relation to the closing pull so that the two curves never intersect. If a shunt coil is used for produc ing the two fluxes, and the maximum currentin the coil is never as great as the value of OD the magnetic force tending to close is always greater than that tending to lock open, assuming that the magnetic circuits correspond to Fig. 2.

In carrying my invention into eflect I utilize a shunt magnetizing coil in this way, and so proportion the two magnetic forces that for the working range of the contactor the closing force produced by the shunt coil is always. greater than the lock-out force produced by it. The magnetic paths of the two fluxes are also so proportioned that the two curves are at the same distance apart (see Fig. 3) while the current in theshunt coil has any value between OG and O-J. The change in the force produced by the look-out part of the flux then exactly balances the changein the closing force due'to variation in the line volts and temperature ofthe coil. Thus the difference between the closing and lock-out forces produced by the shunt coil willbe constant for the working range of the coil corresponding to currents OJ and 0 G, where OG is the maximum current in the coil when maximum line Volts are applied to the coil and the coil is cold, and OJ the current in the coil when minimum line volts are applied and the coil is at maximum temperature.

In addition to this magnet producingtwo opposing forces I use a. magnet energlzed by a series coil, the flux path of which is independent of either of the paths of the flux produced bythe shunt coil. The armaturefor this magnet is mounted on the lever which forms part of the shunt wound magnet, or may be an extension of this lever. Thev arrangementis such that the force due to the series magnet tends to hold the contactor in the open position and the contactor will close when the closing force of the shunt coil is ust greater than the sum of the forces due to the out of balance weight of the movinglever, the look-out force of the series coil, and the lock-out part of the shunt coil flux. As the closing force is made practically constant for the working range of the contactor by the method described above,

the shunt coil; 11 represents the core of;

this; 12 represents the armature for the closing flux; 14 the armature for the lockout part of the flux of this coil; 17 represents the series lock-out coil; 18 the core of this; 19 represents a cap of magnetic material used for altering the length of air gap in the magnetic circuit of the series magnet. The

contactor is shown in the open position, in which case the lever 14 rests against the non magnetic stop 20. The path of that part of the flux produced by 10 which tends to close the contactor, is shown in full line arrow. The part of the flux produced by 10 which tends to lock out the contactor, passes through 16 and is shown by the dotted arrow. The double headed full line arrow indicates the magnetic path of the series lock-outmagnet. A short circuiting copper band may be used around the limb 13 of the magnet to delay the growth of the closing flux, as shown around the corresponding part of Fig. 1, British Patent No. 11,349 of1911; this, however, is not essential to the scheme forming the subject of this specification.

Fig. 7 shows the diagram of the control connections of a non-reversing'series motor, in which the three contactors marked 2, 3 and t'respectively are of the type forming the subject of thisinvention; the contactors close in theforder 1, 2, 3, 4:. The switches marked S S S are auxiliary switches operated by the contactors; each auxiliary switch is opened when its corresponding contactor'is opened, and is closed by the closing of its contactor. These auxiliary switches are usedjto insure the correct-sequence' of closing of the contactors,if the controller isthrown quickly from the off to the fourth "control position, in which case, if these switches were not used all the shunt coils would beenergized at the same time.

the contactor cannot close until the current in the series lock-out coil of this has decreased to the predetermined value. In the same manner contactor 4 will close when the controller is on the fourth point, if the current in its lock-out coil has decreased to the desired value.

In accordance with the provisions of the patent statutes, I have described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention can be carried out by other means.

What I claim as new and desire to secure by Letters Patent of theUnited States, is

1. An electromagnetic switch of the lockout type comprising a movable switch contact operating member and a shunt coil adapted to produce magnetic fluXes through two parallel paths of both of which the movable member forms a part, one of said fluxes tending to close the switch while the other tends to hold it open, the path of the holding open flux having a reluctance of such value that the force tending to close the switch is substantially constant despite and the temperature of the coil, and a series variations in the current in the shunt coil due to variatlons 1n the nnpressed voltage coil having a flux path independent of the flux paths of the said shunt coil for holding the switch open until the current in said series coil drops to a predetermined value.

2. An electromagnetic switch of the lockout type comprising a movable switch contact operating member and a shunt, coil adapted to produce magnetic fluxes through two parallel paths of both of which the movable member forms a part, one of said fluxes tending to close the switch while the other tends to hold it open, the path of the holding open flux having an air gap of such length that the force tending to close the switch is substantially constant despite variations in the current in the shunt coil due to variations in the impressed voltage and the temperature of the coil, and a series coil having a flux path independent of the flux paths of the said shunt coil for holding the switch open until the current in said series coil drops to a predetermined value.

In witness whereof I have hereunto set my hand this 13th day of June, 1919.

HAMMOND CHARLES HASTINGS.

l Vitnesses:

JOHN HALFoRo, DOROTHY WHITE. 

